WASHINGTON – The question that should be at the center of the debate over same-sex marriage is "what is marriage?" argued Sherif Girgis, Ryan T. Anderson and Dr. Robert P. George at a Tuesday Heritage Foundation seminar in Washington, D.C. They are the authors of a new book, What is Marriage? Man and Woman: A Defense.

The reason a lot of conservatives find it difficult to talk about the issue of gay marriage, said Girgis, a Ph.D. candidate at Princeton University and J.D. candidate at Yale Law School, is that "they've accepted the main framing culture has given us – it's about expanding the pool of people able to marry. That's not what this debate is about. ... It's about what marriage is."

There are two separate views of marriage described in the book. The revisionist view, they argue, sees marriage as based upon an emotional union tied to romance. The authors favor what they call the "conjugal view" of marriage, which they define as: "a comprehensive union: a union of will (by consent) and body (by sexual union); inherently ordered to procreation and thus the broad sharing of family life; and calling for permanent and exclusive commitment, whatever the spouses' preferences."

Laws should define marriage according to the conjugal view, they argue, because of the many public goods that benefit society when such a view is upheld and promoted. Law shapes beliefs, beliefs shape behavior, and human well-being and interests are affected by beliefs and behavior, they contend.

The book's argument does not appeal to scripture or religious authority. It also does not make any claims about the morality of homosexuality. Rather, it provides a philosophical defense of the conjugal view of marriage, with supporting evidence from social science studies. While the conjugal view is consistent with the views of monotheistic religions, it can also be found among some secular philosophers, such as Plato and Aristotle, and in civil laws of European traditions, Girgis explained.

Redefining marriage, the authors claim, will bring harm to the many public goods provided by marriage. Among these public goods described in the book, the authors discussed the well-being of children, limited government and religious liberty in the seminar.

A wealth of social science studies support the view that marriage structure matters to the well-being of children, contended Anderson, the William E. Simon fellow in religion and a free society at The Heritage Foundation, and kids do best when raised by a biological mother and father.

Paraphrasing sociologist David Popenoe, Anderson said, "We should get rid of the idea that mommies can be good daddies and daddies can be good mommies."

The conjugal definition of marriage is also necessary for limited government, Anderson argued, because when marriage fails the welfare state necessarily increases to aid the broken lives that result. Citing a study by Brookings Institution, a left-of-center think tank, Anderson noted that between 1970 and 1996, $229 billion in federal welfare expenditures is attributable to the breakdown of marriage. Plus, a 2008 study showed that divorce and unwed parenting cost taxpayers $112 billion per year in state and federal social safety net programs.

Echoing that theme, George, McCormick professor of jurisprudence at Princeton University, said that conservative ideals – "limited government, economic growth, rule of law, and the preservation of democratic self-government" – cannot be maintained "while letting the institution of the family erode and collapse."

"Everything depends on marriage," George said, "because it is the fundamental unit of society, the original and best department of health, education and welfare, supplying what every other institution in society needs, depends on, for its own flourishing, but which none of those institutions can supply for themselves."